10 years ago
See also https://secure.wikimedia.org/wikipedia/en/wiki/Motor-generator
Some of the electric car designs using regenerative braking basically use the wheel motors as generators to recapture some of the braking energy. But the motor, or generator, can only be one or the other at any given time. Or you need a motor driving a separate generator. No, you can't build a perpetual motion machine this way.
At the same time? What are you asking? L
Yes, a high end servo motor contains a motor and a tacho. The Tacho is a precision generator: the output voltage can be converted into accurate speed measurements.